A tracking and telemetry system is known from European patent application EP 0 357 309, which discloses a tracking and telemetry system for tracking personnel in a building or on an industrial estate. The document discloses a tag which can be worn by an employee, which tag periodically transmits a signal that can be received by a field monitoring device (FMD). The tag is capable of generating the signals periodically, wherein the periodicity of the signal can be set by a control module.
One drawback of the device disclosed in EP 0 357 309 is the fact that it is not easy, when in use, to adjust the periodicity to the conditions as they occur. The behaviour of the transmitter is determined by the control module, and consequently said behaviour can only be fixed by programming the control module. This needs to be done for each transmitter individually. In addition, collective adaptation of the behaviour of a multitude of transmitters is not possible.
Such tracking and telemetry systems are furthermore used for tracking, following and/or checking persons or objects in various situations. Examples of this are the geographic monitoring of persons, for example at home, at a home for the elderly or at school, the tracking down of roll containers in a warehouse, the guarding of objects, such as a bicycle, or the monitoring of the state of health of patients in hospital.
A transmitter attached to an object or worn by a person, also referred to as “tag” in English professional literature, transmits a transmitter-identifying signal according to a time schedule, for example periodically, which signal can be received by one or more receivers. The position of the transmitter, or of the object or the person wearing the transmitter, can e.g. be located or tracked, or a particular event can be signalised, for example by delivering an alarm signal in emergency situations or the like.
Locating or tracking the transmitter may be done by means of a positioning technique, using triangulation, in which the location of the transmitter can be computed from the signal received by three or more receivers and their (relative) geographic positions.
Additional information about the object or the person in question may be added to the first signal that is to be transmitted by the transmitter. For example, if the transmitter that is worn by a person is operatively connected to or fitted with a temperature sensor, it will be possible at all times to provide up-to-the-minute information about said person's body temperature. Other applications in this connection are e.g. the registration of the blood pressure, of the heartbeat, of a person or an object falling, of the humidity level, etc., providing that the transmitter is operatively connected to and/or fitted with suitable sensors or input means. When a predetermined limiting value is exceeded, an alarm signal may be automatically generated by the receiver, for example.
Active transmitters usually transmit an identification signal, which is typically detectable over a few hundred metres. The transmitter needs to have its own power supply source, such as a battery, for supplying the energy that is required for that purpose. An important problem in this regard is the life of the battery. In systems that are used in practice, the (service) life of the battery is only about three years in the case of normal use, such as the transmission of an identification signal at intervals of e.g. a few seconds, whilst most applications require a much longer (service) life, e.g. 10 years.
U.S. Pat. No. 5,650,770 discloses a personal alarm system, comprising a transmitter which transmits a signal that can be received by a receiver. The personal alarm system also comprises a number of different sensors, by means of which environmental parameters, such as the presence of smoke, water, high temperatures, carbon monoxide etc. can be measured, and the status of the label and/or the signal can be adjusted on the basis thereof. U.S. Pat. No. 5,650,770 in particular makes mention of the possibility of adjusting the strength of the signal in dependence on the distance between the transmitter and the receiver with a view to saving battery power.
Collective adjustment of the transmitters in this tracking and telemetry system is not possible, whilst it is furthermore necessary for each transmitter to be programmed individually.